Identification and analysis of source emissions through harmonic phase comparison

ABSTRACT

The present invention is a signal processing method to significantly improve the detection and identification of source emissions. More particularly, the present invention offers a processing method to reduce the false alarm rate of systems which remotely detect and identify the presence of electronic devices through an analysis of a received spectrum the devices&#39; unintended emissions. The invention identifies candidate emission elements and determines their validity based on a frequency and phase association with other emissions present in the received spectrum. The invention compares the measured phase and frequency data of the emissions with a software solution of the theoretically or empirically derived closed-form expression which governs the phase and frequency distribution of the emissions within the source. Verification of this relationship serves to dramatically increase the confidence of the detection.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is related to and claims priority from U.S. Provisionalpatent application titled “Identification and Analysis of SourceEmissions through Harmonic Phase Comparison” filed on Oct. 23, 2009 withSer. No. 61/279,605.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not Applicable

REFERENCE TO SEQUENCE LISTING, A TABLE, OR A COMPUTER PROGRAM LISTINGCOMPACT DISK APPENDIX

Not Applicable

BACKGROUND OF THE INVENTION

The present invention is in the technical field of signal processing.More particularly, the present invention is in the technical field ofelectromagnetic signal processing. More particularly, the presentinvention is in the technical field of unintended electromagnetic signalprocessing for the purposes of detecting, identifying and locatingelectronic devices.

Any electronic device necessarily emits electromagnetic radiationunintentionally. These emissions are commonly referred to asElectromagnetic Interference in other contexts and are formed byinternal device signals which radiate from wires and traces which act asantenna elements. Although weak by communications standards, theseradiated signals are unique, consistent and specific to a given device.A sensitive receiver, modern signal processing and a priori knowledge ofthe device's radiated emissions together provide a mechanism to remotelydetect and identify the device. Given a database of electronic deviceemission structures, it is possible to monitor, detect and identify anassortment of electronic devices.

The ability to detect and identify electronic devices provides usefulapplications to both military and commercial applications. For example,electronically triggered improvised explosive devices may be detectedthrough the remote reception and analysis of electronic trigger'sunintended emissions. This application alone is sufficient to motivatethe development of an unintended emissions sensor. However, the growingpervasiveness of electronics in modern society amplifies theseinterests, offering a rich diversity of applications to which devicedetection and identification applies, including security, tracking, andsurveillance.

A previous patent application Ser. No. 12/422,646 filed Apr. 13, 2009“ACTIVE IMPROVISED EXPLOSIVE DEVICE (IED) ELECTRONIC SIGNATUREDETECTION” which is herein incorporated by reference, addressedmethodologies to amplify and distinguish these unintentional emissionsthrough active stimulation of devices from an illumination sourcefollowed by reception of the stimulated emissions. A later patentapplication Ser. No. 12/551,635 filed Sep. 1, 2009 “ADVANCEMANUFACTURING MONITORING AND DIAGNOSTIC TOOL” which is hereinincorporated by reference, addressed the use of unintended emissions tomonitor, verify and predict the health of electronics. Another issuedU.S. Pat. No. 7,515,094 Issued Apr. 7, 2009 “ADVANCED ELECTROMAGNETICLOCATION OF ELECTRONIC EQUIPMENT” which is herein incorporated byreference, addresses additional related methods and devices.

However, the ability to detect these emissions and positively associatethem with a device in the presence of a noisy electromagnetic backgroundis particularly difficult. Received spectral content which is particularto a device must be distinguished from other received signals. Even whenthis is achievable, there often remains doubt as to whether the receivedemissions are in fact related to the targeted device. In particular, itis difficult to identify a device with a low false alarm rate when inthe presence of multiple interferers, or when multiple devices arepresent. Further, it is difficult to dissociate identical devices fromone another such that accurate geo-location may be performed.

BRIEF SUMMARY OF THE INVENTION

The present invention provides a mechanism to detect and identify sourceemissions. More particularly, the present invention is a signalprocessing method to significantly decrease the false alarm rate ofelectronic device sensing systems. More particularly, the presentinvention offers a processing method to reduce the false alarm rate ofsystems which remotely detect and identify the presence of electronicdevices through an analysis of a received spectrum of the devices'unintended emissions. The invention identifies candidate emissionelements in a received spectrum and determines their source based on afrequency and phase association with other emissions present in thereceived spectrum. The invention compares the measured phase andfrequency data of the emissions with a software solution of the knowntheoretically or empirically derived closed-form expression whichgoverns the phase and frequency distribution of the emissions within thesource. Verification of this relationship serves to dramaticallyincrease the confidence of the detection.

The present invention is particularly useful when received emissions ofinterest exist amidst prevalent narrowband background noise. The presentinvention is further useful in dissociating the emissions from similarelectronics when multiple similar devices are within the same region.The present invention can be used to analyze any signal with frequencyand phase related content. Examples include, but are not limited to, theradio-frequency spectrum, audio spectrum, X-rays, Terahertz, andultra-low frequencies.

OBJECTIVES OF THE PRESENT INVENTION

It is therefore one of the primary objects of the invention to providemethod and apparatus using phase relationships between harmonics ofemitted electromagnetic energy to identify that the harmonics are allrelated to the same source.

Another object of the invention is to provide method and apparatus todetect electronic devices by the emissions given off by the devicewhether the emission is intentional or unintentional.

Yet another object of the invention is to provide method and apparatusto identify electronic devices by the emissions given off by the devicewhether the emission is intentional or unintentional.

A further object of the invention is to provide method and apparatus tolocate electronic devices by the emissions given off by the devicewhether the emission is intentional or unintentional.

Yet a further object of the invention is to provide method and apparatusthat determine the instantaneous phase of the underlying source signalso as to identify short term events.

Another object of the invention is to provide method and apparatus todetermine the instantaneous phase of the underlying source signal so asto identify electronically triggered events.

Yet another object of the invention is to provide method and apparatusto determine the instantaneous phase of the underlying source signal soas to discriminate moving targets.

A further object of the invention is to provide method and apparatus todetermine the instantaneous phase of the underlying source signal so asto discriminate fast events.

Yet a further object of the invention is to provide method and apparatusto determine the instantaneous phase of the underlying source signal todetermine the instantaneous phase of the underlying source signal so asto track source emission events.

Still a further object of the invention is to provide method andapparatus to determine the instantaneous phase of the underlying sourcesignal to differentiate harmonic content of a single source from theelectro-magnetic background.

Another object of the invention is to provide method and apparatus thatuse phase relationships between harmonics of emitted electromagneticenergy for remote synchronization.

Yet another object of the invention is to provide method and apparatusthat use phase relationships between harmonics of emittedelectromagnetic energy for calibrating antenna arrays.

Yet a further object of the invention is to provide method and apparatusthat use phase relationships between harmonics of emittedelectromagnetic energy for calibrating distributed antenna arrays.

Still a further object of the invention is to provide method andapparatus that use phase relationships between harmonics of emittedelectromagnetic energy to improve the timing between elements in anantenna array.

Another object of the invention is to provide method and apparatus thatuse phase relationships between harmonics of emitted electromagneticenergy for detecting pulsed power events.

Yet another object of the invention is to provide method and apparatusthat use phase relationships between harmonics of emittedelectromagnetic energy for identifying pulsed power events with aspecific source.

Yet a further object of the invention is to provide method and apparatusthat use phase relationships between harmonics of emittedelectromagnetic energy to perform diagnostics on electronic devices forhealth monitoring.

Still a further object of the invention is to provide method andapparatus that use phase relationships between harmonics of emittedelectromagnetic energy to identify that the harmonics are all related toa specific class of electronic device.

Yet another object of the invention is to provide method and apparatusthat use phase relationships between harmonics of emittedelectromagnetic energy to identify that the harmonics are all related toa high power electrical device.

Yet a further object of the invention is to provide method and apparatusthat use phase relationships between harmonics of emittedelectromagnetic energy to identify that the harmonics are all related toa specific electronic device.

Still a further object of the invention is to provide method andapparatus that use phase relationships between harmonics of emittedelectromagnetic energy to detect a specific electronic device.

Another object of the invention is to provide method and apparatus thatuse phase relationships between harmonics of emitted electromagneticenergy to improve the range of detection of electronic devices.

Yet another object of the invention is to provide method and apparatusthat use phase relationships between harmonics of emittedelectromagnetic energy to improve the confidence of detection ofelectronic devices.

Yet a further object of the invention is to provide method and apparatusthat use phase relationships between harmonics of emittedelectromagnetic energy to enhance the ability to diagnoseElectromagnetic Interference causes.

Still a further object of the invention is to provide method andapparatus that use phase relationships between harmonics of emittedelectromagnetic energy to enhance the Electromagnetic Compatibility oftwo or more electronic devices.

Another object of the invention is to provide method and apparatus thatuse phase relationships between harmonics of emitted electromagneticenergy for use in the Radio Frequency range of frequencies.

Yet another object of the invention is to provide method and apparatusthat use phase relationships between harmonics of emittedelectromagnetic energy for use in the microwave range of frequencies.

Yet a further object of the invention is to provide method and apparatusthat use phase relationships between harmonics of emittedelectromagnetic energy for use in the millimeter range of frequencies.

Still a further object of the invention is to provide method andapparatus that use phase relationships between harmonics of emittedelectromagnetic energy for use in the visible range of frequencies.

Another object of the invention is to provide method and apparatus thatuse phase relationships between harmonics of emitted electromagneticenergy for use in the Extremely Long Frequency range of frequencies.

Yet another object of the invention is to provide method and apparatusthat use phase relationships between harmonics of emittedelectromagnetic energy and a receiver with two or more channels.

Yet a further object of the invention is to provide method and apparatusthat use phase relationships between harmonics of emittedelectromagnetic energy to differentiate between two electronic devicesof the same make and model that are different only by the manufacturinglot.

Still a further object of the invention is to provide method andapparatus that use phase relationships between harmonics of emittedelectromagnetic energy to differentiate and/or identify electroniccomponents on the same circuit board.

Another object of the invention is to provide method and apparatus thatuse phase relationships between harmonics of emitted electromagneticenergy for spectroscopy.

Yet another object of the invention is to provide method and apparatusthat use phase relationships between harmonics of emittedelectromagnetic energy to provide a mechanism for identification of thedevice that is emitting the electromagnetic energy.

Yet a further object of the invention is to provide method and apparatusthat use phase relationships between harmonics of emittedelectromagnetic energy to define that the relationship between theharmonics is the frequency spacing between the harmonics.

Still a further object of the invention is to provide method andapparatus that use phase relationships between harmonics of emittedelectromagnetic energy where small differences between the relationshipbetween the harmonics is used to identify a specific device.

Another object of the invention is to provide method and apparatus thatuse phase relationships between harmonics of emitted electromagneticenergy where the spacing between two or more harmonics are analyzed.

Yet another object of the invention is to provide method and apparatusthat use phase relationships between harmonics of emittedelectromagnetic energy, where higher order harmonics are measured anddifference between higher order harmonics is used to measure smallchanges of the fundamental.

Yet a further object of the invention is to provide method and apparatusthat use phase relationships between harmonics of emittedelectromagnetic energy where higher order harmonics are used to detectan electronic device when the fundamental or lower order harmonics arenot detectable.

Still a further object of the invention is to provide method andapparatus that use harmonics of two fundamental frequencies of emissionsthat are correlated to provide detection of electronic devices.

Another object of the invention is to provide method and apparatus thatuse phase relationships between harmonics of emitted electromagneticenergy to facilitate the detection of IEDs.

Yet another object of the invention is to provide method and apparatusthat use phase relationships between harmonics of emittedelectromagnetic energy, to facilitate the detection of computerequipment.

Yet a further object of the invention is to provide method and apparatusthat use phase relationships between harmonics of emittedelectromagnetic energy to facilitate the detection of vehicles.

Still a further object of the invention is to provide method andapparatus that use phase relationships between harmonics of emittedelectromagnetic energy to facilitate the detection of electronic devicesfrom a vehicle.

Another object of the invention is to provide method and apparatus thatuse phase relationships between harmonics of emitted electromagneticenergy to facilitate the detection of electronic device from an unmannedvehicle or an aerial unmanned vehicle.

Yet another object of the invention is to provide method and apparatusthat use phase relationships between harmonics of emittedelectromagnetic energy to facilitate detection of electronic devicesfrom an unmanned aerial vehicle.

Yet a further object of the invention is to provide method and apparatusthat use phase relationships between harmonics of emittedelectromagnetic energy to facilitate health monitoring of manufacturingequipment.

Still a further object of the invention is to provide method andapparatus that use non-harmonic emissions correlation to detectelectronic devices.

Another object of the invention is to provide method and apparatus thatuse phase relationships between harmonics of emitted electromagneticenergy, enhanced by use of active techniques.

Yet another object of the invention is to provide method and apparatusthat use phase relationships between harmonics of emittedelectromagnetic energy, enhanced by use of illumination techniques.

Yet a further object of the invention is to provide an electromagneticemission measurement device comprising: an antenna, a receiver, at leastone processor, wherein said electromagnetic emission measurement deviceis configured to monitor at least one electrical device by measuring atleast one electromagnetic emission given off by said at least oneelectrical device.

Still a further object of the invention is to provide an electromagneticemission measurement device comprising: an antenna, a receiver, at leastone processor, wherein said electromagnetic emission measurement deviceis configured to monitor at least one electrical device by measuring atleast one electromagnetic emission given off by said at least oneelectrical device and wherein the electromagnetic emission measurementdevice is configured to use phase relationships between harmonics ofemitted electromagnetic energy.

Another object of the invention is to provide an electromagneticemission measurement device configured to include an analog to digitalconverter than can be part of the receiver, part of the processor orimplemented as a stand alone component.

Yet another object of the invention is to provide an electromagneticemission measurement device configured to monitor the phase of theharmonics of emissions of an electronic device for monitoring health ofsuch electronic device.

Yet a further object of the invention is to provide an electromagneticemission measurement device configured to monitor the phase of theharmonics of emissions of an electronic device for at least one ofhealth monitoring, identification, detection, location and geolocaltonof such electronic device.

Still a further object of the invention is to provide an electromagneticemission measurement device configured to monitor harmonic ornon-harmonic content of emissions of an electronic device for at leastone of health monitoring, identification, detection, location andgeolocation of such electronic device.

Another object of the invention is to provide method and device that usephase relationships between harmonics of emitted electromagnetic energy,wherein the electromagnetic emission measurement device is a multiplechannel device configured to monitor the harmonically related phaseinformation of emissions of an electronic device for detection of theelectrical device.

Yet another object of the invention is to provide the electromagneticemission measurement device configured to monitor the RF related phaseinformation of emissions of an electronic device for detection of suchelectronic device.

Yet a further object of the invention is to provide an electromagneticemission measurement device configured to monitor at least one ofmicrowave, millimeter, optical, infrared, and LF related phaseinformation of emissions of an electronic device for detection of suchelectronic device.

Still a further object of the invention is to provide an electromagneticemission measurement device configured to analyze the related phaseinformation of emissions of an electronic device for detection of suchelectronic device in a satellite or an aerospace vehicle.

Another object of the invention is to provide method and apparatus thatuse changes between harmonics of emitted electromagnetic energy toidentify that the harmonics are all related to the same source.

Yet another object of the invention is to provide method and apparatusthat use phase changes between harmonics of emitted electromagneticenergy to identify that the harmonics are all related to the samesource.

Yet a further object of the invention is to provide method and apparatusthat use phase consistency between harmonics of emitted electromagneticenergy to identify that the harmonics are all related to the samesource.

Still a further object of the invention is to provide method andapparatus that use phase relationships between or related to harmonicsof emitted electromagnetic energy to identify that the harmonics are allrelated to the same source combined with time domain techniques.

Another object of the invention is to provide method and apparatus thatuse phase relationships between harmonics and time domain techniques ofemitted electromagnetic energy to identify that the harmonics are allrelated to the same source.

A further object of the invention is to provide method and apparatusthat use phase relationships and autocorrelation related to harmonics ofemitted electromagnetic energy to identify that the harmonics are allrelated to the same source.

Still a further object of the invention is to provide method andapparatus that measure amplitude and phase relationships and ofharmonics simultaneously of emitted electromagnetic energy to identifythe source of the emission.

Another object of the invention is to provide method and apparatus thatmeasure and compare amplitude and phase relationships of harmonicssimultaneously of emitted electromagnetic energy to identify the sourceof the emission.

Yet another object of the invention is to provide method and apparatusthat measure and compare any combination of amplitude and phaserelationships of emission signature harmonics simultaneously of emittedelectromagnetic energy to identify the source of the emission.

Yet a further object of the invention is to provide method and apparatusthat use measurement of the phase relationships of signatures of emittedelectromagnetic energy to identify the source of the emission.

Still a further object of the invention is to provide method andapparatus that use measurement of the phase relationships of signaturesof emitted electromagnetic energy to locate, detect and/or geolocate thesource of the emission.

Another object of the invention is to provide method and apparatus thatuse measurement of the phase relationships of signatures of emittedelectromagnetic energy to detect or geolocate the source of theemission.

Yet another object of the invention is to provide method and apparatusthat use measurement of the phase relationships of signatures of emittedelectromagnetic energy combined with Doppler effects on a movingplatform to detect the source of the emission.

Yet a further object of the invention is to provide method and apparatusthat use phase relationships between harmonics of emittedelectromagnetic energy combined with a geospatial overlay to improvevisualization of the displayed data.

Still a further object of the invention is to provide method andapparatus that use phase relationships between harmonics of emittedelectromagnetic energy to detect computers, cellular telephones orcommunication devices.

Another object of the invention is to provide a method that uses phaserelationships between harmonics of emitted electromagnetic energy andthat is configured for use in automated algorithms or analog systems.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIG. 1 depicts one embodiment of an unintended emission sensor;

FIG. 2 depicts a received unintended emission pattern.

FIG. 3 depicts a square wave and its associated Fourier seriescomponents;

FIG. 4 depicts a flow-chart of the preferred embodiment of the presentinvention for verifying electronic device presence; and

FIG. 5 depicts the results of an analysis with the preferred embodimentof the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the drawings, in FIG. 1 there is shown a specificembodiment of a system 102 for the detection of source emissions,specifically the detection of unintentional emission from electronicdevices. The system 102 is used to capture electromagnetic emissionswith the intention of identifying the existence of an electronic device114. The system detects electromagnetic radiation 116 which radiatesunintentionally from a device 114. The radiation 116 is detected throughuse of an antenna 118. The detected radiation is amplified above thebackground noise through use of a low noise amplifier 112 to generate areceived signal. The received signal is then filtered 110 to preventsignal aliasing and reduce the noise bandwidth of the signal. The signalis then received 108 to reveal the in-phase (I) and quadrature (Q)components and digitized through the use of an analog-to-digitalconverter 106. The digitized output is analyzed with a processor 104 toreveal the phase and magnitude information of the received signal.

Referring now to FIG. 2, a typical device emission spectrum 202 isdepicted as measured through use of a receiving system 102. Theindividual device emissions 204 radiate from wires and traces inside ofthe device. The emissions are typically the distinct components of acomplex underlying time-domain signal within the device. The underlyingtime-domain signal is composed of multiple single-frequency signals.These single-frequency signals are referred to as the Fourier series ofthe time-domain waveforms and are well known in the art. The system 102detects a subset of these individual emissions 204 to identify thedevice.

Referring now to FIG. 3, a square-wave, which is an example of a commoncomplex time-domain waveform found in electronic devices, is depicted302 with a periodicity of 1/f_(f). The emission components may berepresented mathematically by a Fourier series of the time-domainwaveform. The Fourier series of a square wave 302 is composed of sinewaves 304 at odd harmonic indices. Each sine wave has an argument whichis a function of the harmonic index, k, the fundamental frequency,f_(f), and the evaluated function time, t., as shown in Equation 1:

$\begin{matrix}{{\sum\limits_{{k = 1},3,{5\mspace{14mu}\ldots}}^{\infty}{\sin\left( {\left( {k,f_{f},t} \right)} \right)}} = {\sum\limits_{{k = 1},3,{5\mspace{14mu}\ldots}}^{\infty}{\sin\left( {{k \cdot 2}{\pi \cdot f_{f} \cdot t}} \right)}}} & (1)\end{matrix}$

The Fourier series components have phase values which are periodic withthe period of the time-domain signal. In Equation 1, the time t=0 isequivalent to the rising edge 308 of the square-wave 302; t=½*f_(f) isequivalent to the falling edge 310 of the square-wave 302; and t=1/f_(f)is the time of a next rising edge of the square-wave 302. For asquare-wave, the Fourier series components each begin with a phase of 0radians at t=0 306. As t is increased, each Fourier series componentcycles through phase values 0 to 2π for a number of times dependent onthe harmonic number, k, until each reaches a phase value of 0 radians att=1/f_(f).

An additional example of a device time-domain waveform is the waveformgenerated in the time-domain by the summation of inter-modulationcomponents within a device. For example, a push-pull LC oscillator isknown to produce both a desired frequency, f_(o), and a series ofundesired frequencies at integer multiples. These signals may be viewedas an aggregated complex periodic time-domain waveform and representedby a Fourier series of single-frequency waves. The Fourier series may beconstructed through measurement and analysis of the time-domain waveformor through multiple measurements of the single-frequency components.Further, it is clear to anyone skilled in the art that any complexperiodic time-domain signal may be represented as a series of sine termswherein the constituent cosine terms may be expressed as sine terms witha π/2 phase shift and combined with sine terms of the same frequency.

The relationship of the instantaneous phase and the frequency of each ofthe waveforms in the series persist as the signals are radiated from thedevice 114 and propagate through the air 116. The path length from thedevice to the receiving element is identical for all emissions, even inthe cases where the device 114 or the receiving instrument 102 or bothare in motion; therefore, if the device emissions are collectedsimultaneously or at precisely known times relative to one another, thephase and frequency relationship of the emissions is preserved. Whencollected under these circumstances, all emission components collectedwill have phase and frequency values related to one another as definedby the Fourier series of the complex time-domain signal within thedevice.

If a particular component at harmonic k=k_(x) of the Fourier series ofany particular source waveform is detected by a system 102 and the phaseis measured as θ=θ_(x), there exist a finite number of time values in asingle period of the time-domain waveform at which the particularemission component may take on this measured phase. That is, harmonick_(x) will cycle one or more times through phase values of 0 to 2πwithin a single period of the time-domain waveform and, further,harmonic k_(x) will have an instantaneous phase of precisely θ_(x) onceduring each cycle of the harmonic and therefore one or more times duringthe source period. However, practical considerations in systemresolution and the received signal strength require the addition of anerror term, δ=δ_(x), to this phase measurement, effectively creating arange of phase values, θ_(x)±δ_(x), rather than a precise value, θ_(X).The error term is derived empirically such that the defined phase range,θ_(x)±δ_(x), contains the true phase value. The times within a singlesource waveform period at which the harmonic k_(x) has an instantaneousphase within the phase range θ_(x)±δ_(x) is denoted with vector t=t_(x).This time vector, t, may be identified through a solution to thefollowing equation:Find t such that: |(ℑ(k,f _(f) ,t)modulus 2π)−θ|<δ  (2)where ℑ(k₁,f_(f),t) is the argument of the sine terms of the Fourierseries expression for the complex time-domain waveform and t is a seriesof time values, uniformly separated, within the boundaries of t=0 andt=1/f_(f). If a second component at harmonic k=k_(y) of the Fourierseries of this same complex time-domain waveform is detectedsimultaneously by the system 102 and the phase is measured as θ=θ_(x),with an error of ±δ_(y), the solution of Equation 2 will again yield afinite number of time values, denoted with vector t_(y), at which thisphase may occur in a single period of the time-domain source waveform.The intersection of the values in t_(y) and t_(x) yields a reducedvector of time values, t_(int). The time values within the vectort_(int) are the times within a single period of the source time-domainwaveform at which harmonics k_(x) and k_(y) have an instantaneous phasewithin the measured phase ranges, θ_(x)±δ_(x) and θ_(x)±δ_(x)respectively. Any additional harmonic, k_(z), may be further includedthrough measurement and the use of Equation 2 to obtain an additionaltime vector, t_(z). This vector, t_(z), may be intersected with thevector t_(int) to form a new reduced intersection vector of time values,t_(int)′.

Interfering emissions which are included in this analysis will oftenyield an empty set, { }, in the intersection solution, t_(int). An emptyset in the intersection implies with high certainty that the receivedemissions are not all emitted from a source with the modeled Fourierseries.

The Fourier series model of a time-domain waveform of a targeted deviceis further useful to overcome device variations issues. Electronicemissions are known to vary in the fundamental frequencies of theirinternal time-domain waveforms due to both thermal and manufacturingvariations. Any variation in the fundamental frequency of thetime-domain signal causes even larger variations in the frequency of thehigher-order Fourier series terms. These variations complicate thereception of any given harmonic emission when a system 102 attempts toidentify received emissions. The harmonics themselves, however, arerelated in frequency to one another based on the Fourier series of thetime-domain waveform. That is, the frequency values of the harmonics aremodified through a change in the fundamental frequency, f_(f), but therelationship between harmonic frequencies is undisturbed. Therefore, thefrequency of any emission element may be identified given the frequencyof any other harmonic element through:

$\begin{matrix}{f_{b} = {f_{a} \cdot \frac{k_{b}}{k_{a}}}} & (3)\end{matrix}$

Equation 3 may be applied to any received harmonic to predict thelocation of additional harmonic emissions. The preferred embodiment ofthe present invention searches a spectral region to identify a candidateemission element which is preliminarily assigned to be part of a Fourierseries emitted from a source. Additional emissions are predictedaccording to Equation 3 and, if present, the received emissions areverified for association with the source through use of the phaserelationships detailed in Equation 2. If the additional harmonics arenot present, or the measured phases of the harmonics are not verifiedwith the Fourier series model, the candidate is classified asinterference unrelated to the source.

Referring now to the drawing of FIG. 4, a flow-chart of the preferredembodiment of the present invention is given. A particular device with apre-characterized emission pattern and pre-characterized variation isselected for detection. Emissions are received with a sensor system 102in an electromagnetically noisy environment 402 and electromagneticenergy is detected, digitized and processed for phase and frequencyinformation 404. A particular spectral region of the received energywhich spans the expected emission variation of harmonic k_(a) of thedevice is identified 406. A candidate emission, if present, is selectedfrom this region for analysis 406. The frequency of the candidateemission is then taken and recorded to memory as f_(a) within the system408.

The frequency location of the candidate emission at f_(a) is used todetermine the precise location of additional harmonic emission elements.Harmonic k_(b) is predicted to at frequency f_(b)=f_(a)*k_(b)/k_(a) 410,while harmonic k_(c) is predicted to be at frequencyf_(c)=f_(a)*k_(c)/k_(a) 412. If an emission element is not presentwithin the received spectrum at either frequency f_(b) or f_(c), thecandidate emission is classified as interference and a different initialcandidate emission within the region of interest is chosen 406. Theprocess is repeated until either: all candidate emissions within theregion of interest are exhausted, in which case the targeted electronicswas not identified; or the two additional harmonics k_(b) and k_(c) areidentified.

If both of the additional harmonic emission elements k_(b) and k_(c) doexist in the predicted frequency range centered about frequencies f_(b)and f_(c), a measurement of each emission's phase is taken 414. Eachphase value is ascribed an error boundary, ±δ, which effectively changesthe phase value to a phase range centered about the measured phase value414. The error term is defined for the system based on the measurementsensitivity such that the defined phase range will contain the truephase of a measured signal.

A comparison of the phases of the emissions is then made through thefollowing process to significantly reduce the false alarm rate of thesystem, effectively allowing detection and identification of signalswithin considerably noisy backgrounds. Each of the phase ranges forharmonics k_(a), k_(b), and k_(c), and their associated measuredfrequencies, f_(a), f_(b), and f_(c), are applied to the known model ofa Fourier series of emissions of the targeted device. The model assumesa single period of the fundamental tone, 1/f_(f) in duration, wheref_(f)=f_(a)/k_(a), which begins at t=0. A series of time vectors isgenerated for each emission, {t_(a), t_(b), t_(c)}, as follows:Find t _(a) such that: |(ℑ(k _(a) ,f _(f) ,t _(a))modulus2π)−θ_(a)|<δ_(a)Find t _(b) such that: |(ℑ(k _(b) ,f _(f) ,t _(b))modulus2π)−θ_(b)<δ_(b)Find t _(c) such that: |(ℑ(k _(c) ,f _(f) ,t _(c))modulus2π)−θ_(c)|<δ_(c)

The vectors t_(a), t_(b) and t_(c) define the times within the sourcetime-domain waveform period, from t=0 to t=1/f_(f), at which themeasured emissions at frequencies f_(a), f_(b), and f_(c) may havemeasured instantaneous phases within the phase ranges of θ_(a)±δ_(a),θ_(b)±δ_(b), and θ_(c)±δ_(c) 416. The intersection of the time vectorst_(a), t_(b) and t_(c) yields a vector t_(int) of times at which thephase ranges of the harmonic emissions may occur simultaneously. If asingle time solution, or more than one time solution, exists withint_(int) 418, the measured emissions are consistent with the time-domainwaveform of the device and the target is considered identified 420.Positive association of the phases of any harmonic signal with two otherharmonic signals implies with high certainty that the analyzed signalsare harmonics which originated from a single source, rather thanindependent signals or noise sources. The decision process 418 is statedas:

If intersection of {t_(a), t_(b), t_(c)}≠empty set, the measuredharmonics are predicted to have originated from the targeted sourcedevice 420.

If intersection of {t_(a), t_(b), t_(c)}=empty set, the measuredharmonics are predicted not to have originated from the targeted sourcedevice and a new candidate emission is chosen for analysis from thespectral region of k_(a) 406.

Referring now to FIG. 5, depicted is the results of an analysis of aphase comparison on a 20 MHz square-wave. The 39^(th) harmonic isidentified at a frequency of 780 MHz and found to have a phase of 3.0radians with a measurement uncertainty of 0.05 radians. The 49^(th)harmonic is simultaneously received with the 39^(th) harmonic and foundto have a phase of 1.0 radian with a phase uncertainty of 0.05 radians.The intersection of the time solutions to the Fourier series, asdescribed above, is evaluated. All harmonics from the 50^(th) to the99^(th) are then examined to determine the required phase values at theintersection times for these harmonics to be part of the harmonicseries. As shown in FIG. 5, the phase of any third chosen harmonicbetween k=50 and k=99 will be defined to reside within a narrow phaseregion. FIG. 5 depicts possible phase values of a third harmonic inwhite and not-possible phase values in black. Therefore, a thirdemission measurement at any of these harmonics is required to have ameasured phase range within the region defined in FIG. 5 for a positiveprediction of association with the targeted source to be made.

The specific embodiment expressed through reference to the flow chart ofFIG. 4 is not intended to limit the application of this technique. It isclear to anyone skilled in the art that variations on the above specificembodiment may be applied. For example, although the preferredembodiment for the present invention makes use of three harmonics, thepresent invention may be applied to only two signals within the spectrumto provide a meaningful verification of the emission relationship or toreject interfering signals. Similarly, the present invention may beapplied to more than three harmonics to yield increased confidence andincreased precision in the instantaneous phase of the device'stime-domain signal. Irrespective of the number of harmonic emissionsanalyzed in the present invention, the precision of the results of thepresent invention are dependent on the selection of the harmonic indicesfor reception. That is, certain choices of received harmonic emissionsresult in an intersection vector, t_(int), with fewer values than otherchoices of received harmonic emissions.

A benefit of this processing technique is that with repeatedobservations of the emissions there is a continued increase in theconfidence of the prediction of target presence and identity. Phaserelationships are expected to change if the emissions are not in factrelated through an underlying time-domain waveform. Therefore, repeatedobservations and verifications of the phase relationship betweenreceived emissions serves to reduce the likelihood that the measuredemissions are coincidentally present at the expected frequencies andcoincidentally have the appropriate phases needed for association with atargeted device.

Further, it is considered that if the phases of the source emissions areverified through the present invention with three or more harmonics, theinstantaneous position within a single period of the target'stime-domain signal is determined. For example, the use of threeharmonics in the present invention defines a short, contiguous vector oftime values, t_(int), which resides within the period of the time-domainwaveform from t=0 to t=1/f_(f). If the analyzed source were theunintended emissions of an electronic clock, the transition edges ofthis clock source may be easily determined, with an error based on thelargest and smallest values within t_(int). Tracking the location withinthe fundamental period of a remote source allows precise remotesynchronization between devices allowing, for example, phase timing inwidely separated array receivers, or timed analysis of short durationevents for which knowledge of the source phase is relevant. Thisinformation is further useful in directed energy applications whichwould benefit from synchronizing the pulses of a directed energy weaponwith the target's internal functionality.

An additional benefit of the present invention is that it may be used tomitigate interfering signals while on a moving platform or whenreceiving from a moving source. The aforementioned phase and frequencyrelationships between received harmonics will be maintained independentof any motion induced Doppler shifting. In addition, interfering signalswill vary in phase differently when they are not geometricallyco-located with the source of interest. Therefore, relative Dopplershifting of the harmonics and interferers, which is apparent in afrequency and phase analysis of the receive emissions, allows for thediscrimination between sources with higher accuracy than available froma static separation. When the interfering signals are from a similardevice, the Doppler effect from the relative motion serves to improvedifferentiation between the two devices.

Moreover, the present invention may be used to improve the geolocationof detected electronics by providing a improved resolution of thereceived phase of the source emissions through the analysis of theirmutual relation.

An additional benefit of the present invention is that the receivedemission elements may be considerably higher frequency (harmonicindex>>1) than the fundamental harmonic of the source for operation. Anyharmonic signals of the emission pattern which may be received by thesensing system may be used by the present invention. A benefit of thisability of the invention is that it allows for the verification of thedevice presence through only the narrowband reception of a few emissionsin any particular frequency range, often desirable due to limitations inantenna size and performance in a sensing system.

In a broad embodiment, the present invention is a method to identify anemission source through an analysis of the relation of the phase andfrequency of a subset of the received emissions with a model of theFourier series of the emission waveform. The invention may be applied toany emission content which is composed of a pattern of frequencies withrelated phases, including without limitation the emissions of x-rays,terahertz waves, millimeter waves, radio waves, microwaves, opticalwaves, infrared waves, low frequency waves, and sonic waves.

While the foregoing written description of the invention enables one ofordinary skill to make and use what is considered presently to be thebest mode thereof, those of ordinary skill will understand andappreciate the existence of variations, combinations, and equivalents ofthe specific embodiment, method, and examples herein. The inventionshould therefore not be limited by the above described embodiment,method, and examples, but by all embodiments and methods within thescope and spirit of the invention as claimed.

We claim:
 1. A method comprising: receiving an electromagnetic energyemission with an antenna connected to a receiver; and using a processorto: select a candidate harmonic of a device from an expected spectralregion of the electromagnetic energy emission, use a frequency locationof the candidate harmonic to determine frequency locations of additionalharmonics, identify, from the received electromagnetic energy emission,at least two of said additional harmonics, measure a phase of eachharmonic, and compare the measured phases to identify the device as asource or a non source of the electromagnetic energy emission.
 2. Themethod of claim 1, wherein said electromagnetic energy emission is anunintended electromagnetic emission.
 3. The method of claim 1, whereinsaid electromagnetic energy emission is an intended electromagneticemission.
 4. The method of claim 1 wherein said method is used to locateor geolocate said device.
 5. The method of claim 1, wherein said methodis used to determine an instantaneous phase of an underlying sourcesignal to identify at least one short term event.
 6. The method of claim1, wherein said method is used to differentiate harmonic content of saidsource from electro-magnetic background noise.
 7. The method of claim 1,wherein said method is used for detection of at least one electronicallytriggered event.
 8. The method of claim 1, wherein said method is usedto perform diagnostics on an electronic device, an electrical component,and a combination thereof for health monitoring.
 9. The method of claim1, further comprising the step of actively illuminating said device. 10.The method of claim 1, wherein said method is used to identify that aset of harmonics are all related to a specific class of electronicdevice.
 11. The method of claim 1, wherein said method is used toidentify that a set of harmonics are all related to a specificelectronic device.
 12. The method of claim 1, wherein said method isused to aid in spectroscopy.
 13. The method of claim 1, wherein saidsource is an electrical device.
 14. The method of claim 1, wherein saidprocessor is further used to add an error term to each phase measurementand change said each phase measurement to a phase range measurement. 15.The method of claim 1, wherein said processor is further used tocalculate a time vector for each harmonic and to plot time vectors in atime-domain waveform.
 16. The method of claim 15, wherein said processoris further used to intersect said time vectors, to identify anintersecting vector and to determine a value of said intersectingvector.
 17. The method of claim 1, wherein said processor is furtherused to classify said electromagnetic energy emission as interference inabsence of said frequency locations for said at least two additionalharmonics.
 18. A device comprising: an antenna, a receiver connected tosaid antenna and configured to receive an electromagnetic energyemission, and at least one processor configured to: select a candidateharmonic of a device from an expected spectral region of theelectromagnetic energy emission, use a frequency location of thecandidate harmonic to determine frequency locations of additionalharmonics, identify, from the received electromagnetic energy, at leasttwo of said additional harmonics, measure a phase of each harmonic, andcompare the measured phases to at least one of identify the device as asource or a non source of said electromagnetic energy emission.
 19. Theelectromagnetic emission measurement device of claim 18, wherein theelectromagnetic emission measurement device is configured to include ananalog to digital converter that is part of a receiver, part of said atleast one processor, or implemented as a stand alone component and acombination thereof.
 20. The device of claim 18, wherein said processoris further configured to add an error term to each phase measurement andchange said each phase measurement to a phase range measurement.
 21. Thedevice of claim 18, wherein said processor is further configured tocalculate a time vector for each harmonic and to plot time vectors in atime-domain waveform.
 22. The device of claim 21, wherein said processoris further configured to intersect said time vectors, to identify anintersecting vector and to determine a value of said intersectingvector.
 23. The device of claim 18, wherein said processor is furtherconfigured to classify said electromagnetic energy emission asinterference in absence of said frequency locations for said at leasttwo additional harmonics.
 24. A method comprising the steps of: (a)receiving unique harmonic spectral regions of an electromagnetic energyemission with an antenna connected to a receiver; (b) selecting, with aprocessor, from an expected spectral region of frequencies received instep (a), a candidate harmonic of a device; (c) determining, with saidprocessor, a frequency location of said candidate harmonic; (d)determining, with said processor from said unique harmonic spectralregions received in step (a) and based on said frequency location ofsaid candidate harmonic determined in step (c), frequency locations forat least two additional harmonics, each from a respective uniquespectral region received in step (a); (e) measuring, with saidprocessor, phase values of said candidate and said at least two otherharmonics selected or determined in steps (b) and (d); and (f)determining, with said processor in accordance with at least one logicalgorithm, a time phase relationship of said candidate and said at leasttwo additional harmonics to identify said device as a source or a nonsource of said electromagnetic energy emission.